Articulated Bone Screw Head for Acetabular Implant Stability

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Solution Overview

Problem

Existing hip-joint acetabular implants face challenges with bone screw anchoring, including limited angular freedom, risk of screw head protrusion, and screwdriver jamming, especially in thin-walled implants, which can lead to unstable anchoring and early implant failure.

Innovation Solution

A bone screw with an articulated head and a hip-joint acetabular implant featuring a slotted hole allows for greater angular freedom and stable anchoring, preventing screw head protrusion and jamming through a two-part head design with a ball joint-like connection, enabling varied orientation and positioning of the screw shaft relative to the implant.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a bone screw is used with a hip-joint acetabular implant, then stable anchoring in the pelvic bone is achieved, but the bone-screw head may protrude into the interior of the implant when tilted, preventing stable anchoring of the inlay

Engineering Contradiction:

Improvestable anchoringVSAvoidangular freedom

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The bone screw head is designed with a two-part articulated structure comprising a head piece and a separate head carrier that can pivot relative to each other. This dynamic joint allows the bone-screw shaft to assume different orientations while the head piece maintains stable contact with the implant surface, resolving the contradiction between anchoring stability and angular adaptability

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The head of the bone screw is divided into two functional parts: a head piece that contacts the implant and a separate head carrier that interfaces with the bone. This segmentation allows independent optimization of each part's function, enabling the head piece to remain stationary on the implant while the head carrier adapts to various bone angles

Inventive Principle:

Principle #1Segmentation

2Reliability

If the bone screw junction is designed to be robust to prevent screwing through, then anchoring stability improves, but the screwdriver may become jammed due to deformation of the bone-screw head during tightening

Engineering Contradiction:

Improveanchoring stabilityVSAvoidscrewdriver operation

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The articulated head design allows the head carrier to pivot and absorb deformation forces during screw tightening, preventing stress concentration that would cause head deformation and screwdriver jamming, while still maintaining robust anchoring stability

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The pivot joint between the head piece and head carrier acts as a cushioning element that absorbs and distributes tightening forces before they can cause deformation of the bone-screw head, preventing screwdriver jamming before it occurs

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Adaptability or versatility

If special screw holes with conical bores are provided to allow angular play, then bone-screw positioning freedom increases, but the production complexity and surgical effort increase

Engineering Contradiction:

Improvepositioning freedomVSAvoidimplant structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

Instead of making the implant hole complex to accommodate screw angulation, the invention inverts the approach by making the screw head itself articulated and adaptable. The simple round hole in the implant works with the flexible screw head design to achieve the same positioning freedom

Inventive Principle:

Principle #13The other way round (Inversion)

4Adaptability or versatility

If the bone screw allows high angular freedom for optimal bone anchoring, then screw placement flexibility improves, but the risk of screw head protrusion into the implant interior increases

Engineering Contradiction:

Improvescrew placement flexibilityVSAvoidscrew head protrusion

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The articulated head allows the bone-screw shaft to pivot and achieve optimal angulation for bone anchoring, while the head piece remains constrained to maintain stable contact with the implant surface, eliminating the harmful protrusion effect

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The pivot joint between the head piece and head carrier acts as an intermediary mechanism that decouples the angular movement of the shaft from the contact position of the head, allowing flexibility without protrusion

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11123123B2Medical bone screw and implant system

Publication Date: 2021.09.21 AESCULAP AG

AI summary

An implant system includes an acetabular implant and a bone screw having an articulated screw head which allows an unchanged contact position of the screw head on the acetabular implant when the bone screw is aligned relative to the acetabular implant. For this purpose, a slotted hole is made in the acetabular implant in which slotted hole the bone screw can be pivoted in longitudinal direction of the slotted hole.